Decreased antibiotic action of tetracyclines & quinolones. Decreased absorption of levodopa, levothyroxine, bisphosphonates, methyldopa, penicillamine. Reduced Fe absorption w/ antacids & PPI, some food (eg, tea, coffee, wholegrain cereals, eggs & milk), oral neomycin, Ca, Zn & oral Mg salts, bicarbonates, carbonates, oxalates & phosphates.